Sampling and analysis of sulfur compounds

ABSTRACT

A method for accurately sampling ambient air containing sulfur compounds in the low parts per billion range and for separating, identifying and quantitatively monitoring each sulfur compound. The gaseous sample is collected in substantially sulfur-free methanol. The methanol solution is then passed through a gas chromatograph column packed with octylphenoxypolyethylene on oxyethanol polytetrafluoroethylene to separate the sulfur compounds. From the gas chromatograph the separated sulfur compounds go through a pyrolysis furnace where they are oxidized to sulfur dioxide, and thence into a microcoulometer for titration. By using the same procedure, sulfur compound impurities in solid materials can be identified and quantitatively measured.

iJnited States Patent Eads [451 Mar. 211, i972 SAMPLING AND ANALYSIS OFSULFUR COMPOUNDS.

Ewin A. Ends, Beaumont, Tex.

[72] Inventor;

[73] Assignee: Lamar State College of Technology, Beaumont, Tex.

[22] Filed: Sept. 8, 1970 [21] Appl. No.: 70,478

[52] U.S. CL. ..23/230 PC, 23/232 C [5|] Int.Cl. ..G01n31/08,G0ln3l/l6[58] Field of Search ..23/230 PC, 232, 254, 232 C, 23/230 [56]References Cited UNITED STATES PATENTS 3,529,937 9/1970 lhara et al...23/230 PC X OTHER PUBLICATIONS Glass et aL, Anal. Chem. 32, No. 10,September 1960, 1,265-

Primary Examiner-Morris O. Wolk Assistant Examiner-11. M. ReeseAttorney-Bertram H. Mann, Frank B. Pugsley, James G. Ulmer, Delmar L.Sroufe and Larry B. Feldcamp [57] ABSTRACT A method for accuratelysampling ambient air containing sulfur compounds in the low parts perbillion range and for separating, identifying and quantitativelymonitoring each sulfur compound. The gaseous sample is collected insubstantially sulfur-free methanol. The methanol solution is then passedthrough a gas chromatograph column packed with octylphenoxypolyethyleneon oxyethanol polytetrafluoroehtylene to separate the sulfur compounds.From the gas chromatograph the separated sulfur compounds go through apyrolysis furnace where they are oxidized to sulfur dioxide, and thenceinto a microcoulometer for titration.

By using the same procedure, sulfur compound impurities in solidmaterials can be identified and quantitatively measured.

10 Claims, 1 Drawing Figure l SAMPLING AND ANALYSIS OF SULFUR COMPOUNDSLICENSE TO THE U.S. GOVERNMENT A non-exclusive, irrevocable,royalty-free license in the invention herein described, throughout theworld for all purposes of the U.S. Government, with the power to grantsublicenses for such purposes, is hereby granted to the Government ofthe United States of America.

BACKGROUND OF THE INVENTION air pollution control work in the scientificcharacterization of odors from sulfur compounds.

2. Description of the Prior Art One of the primary sources of odorpollution are sulfur compounds, such as carbonyl sulfide, hydrogensulfide and various organic sulfur compounds. The term organic sulfurcompounds as used herein and in the art is intended to designate a groupof compounds of thetype RSH, RS H, R 5, and R 8 in which R represents analiphatic or aromatic radical. One or more of these sulfur compounds areemitted by rendering plants, kraft paper mills, oil refineries, Fraschsulfur plants and various chemical plants.

The odor thresholds for carbonyl sulfide, hydrogen sulfide and mostorganic sulfur compounds are generally regarded as being in the rangefrom about 0.4 to about 4.0 parts per billion. Because of these low odorthresholds, it has been found almost impossible to scientificallycharacterize levels of odor emissions for these sulfur compounds. Thishas resulted from the inability to accurately sample,'separate, identifyand quantitatively monitor mixtures of sulfur compounds in the low partsper billion range.

The primary reason that has deterred the development of analyticaltechniques for low concentrations of sulfur compounds is the reactivenature of sulfur, especially with respect to sampling and separatingsulfur compounds. Sulfur compounds have a tendency to adhere to or reactwith the surface materials of the sampling and analytical equipment,and/or react with the liquid or gaseous materials in the equipment.Obviously, the accuracy of concentration measurements in the low partsper billion range is substantially affected by the ability to preventsulfur compounds from reacting with or adhering to other materials.

The difficulties encountered in developing techniques for sampling andanalyzing low concentrations of sulfur compounds have hindered thedevelopment of satisfactory odor regulations by air pollution controlagencies. Most, if not all, air pollution control agencies that haveeven attempted to regulate the emission of odors use one form or anotherof odor pollution panels, which usually consist of three or more personssmelling air samples to determine if the odors are, offending.Obviously, the determinations made by these odor pollution panels aresubject to the variations of the human nose and lack the desiredscientific characterization typical of most air pollution controlregulations.

In addition, progress in the development of methods and equipment forcontrolling the emission of odor-causing sulfur compounds has beendelayed by the aforementioned difficulties. Identification of the sulfurcompounds that are being emitted and a determination of theconcentrations of these compounds are prerequisites to the developmentof techniques and equipment to abate the emissions of odor pollutants.

Most methods for measuring sulfur compounds that have gained anyacceptance in air pollution control work are restricted to those whereonly one specific sulfur compound is measured. For example, hydrogensulfide can be measured by using either the lead acetate tape method orthe cadmium acetate-acetic acid absorption method has been developed formethyl mercaptan.

A more flexible instrument which separates and quantitatively monitors atwo or more sulfur compounds is the recently developed Barton titrator.In this instrument the gas is impinged through a series of chemicalsolutions which selectively extract the various sulfur compounds in thegas sample. However, this instrument does have the limitation of notbeing capable of separating some organic sulfur compounds. Furthermore,the use of a Barton titrator for analyzing low concentrations of sulfurcompounds is a relatively slow method in that each chemical solutionwhich is used to extract a specific sulfur compound or group ofcompounds must be titrated separately with a microcoulometer. Anadditional problem is that the complexes formed in the chemical solutionupon the extraction of the sulfur compound or compounds are relativelyunstable, requiring therefor almost immediate titration to avoid anyloss of accuracy.

Generally, previous attempts to separate sulfur compounds with gaschromatograph columns have proved to be unsuccessful because of thetenacious adherence of sulfur compounds to the column walls or solidsupports, or irreversible reactions with the column walls, supports,stationary liquid phase or carrier gas. For example, in a paperpresented at the 157th meeting of the American Chemical Society inMinneapolis, Minn., in April of 1969, Stevens and others related suchdifficulties with columns packed with 10 percent Triton X-30S(octylphenoxypolyethylene oxyethanol) or Fluoropart T(polytetraflouoroethylene). However, as described in a recent article,Modem Aspects of Air Pollution Monitoring," by Stevens and OKeeffe,Analytical Chemistry, Volume 42, No. 2, Feb. 1970, an automatedanalytical gas chromatograph system has been developed which canquantitatively measure low parts per billion levels of sulfur dioxide,hydrogen sulfide, methyl mercaptan and ethyl mercaptan in ambient air.

Although this chromatographic system seems to obviate the disadvantagesof the Barton titrator, as noted above, its accuracy, as is the Bartontitrators, is dependent upon the sampling technique used. The possibleinaccuracy results from the tendency of gaseous sulfur compounds toadhere to and/or react with the walls of the gas-sampling containers,regardless of the material used. As mentioned previously, even thesmallest loss of material resulting from any adherence or reaction willcause substantial inaccuracy when measuring concentrations in the partsper billion range.

Obviously, the loss of accuracy can be minimized by directly injectingthe gas sample into the analyzing equipment. However, this would requirehaving the analyzing equipment at the point of sampling. Thisrequirement of using sensitive analyzing equipment in the field hasseveral disadvantages. Since the analyzing equipment would be surroundedby the atmosphere to be analyzed, any leakage in the equipment couldsubstantially affect the results. Obviously, the more the equipment istransported from sampling point to sampling point, the greater thepossibility of leakage and the more time required for maintenance.Furthermore, when numerous samples are required, the use of sensitiveanalyzing equipment in the field is much more expensive, both in termsof the number of trained personnel and the amount of equipment required,than if the samples were collected in the field by relatively untrainedpersonnel and taken to a central laboratory for analysis. At such acentral laboratory the samples could be run on more or less a continuousbasis under controlled atmospheric conditions. In this manner, expensiveanalyzing equipment can be more efficiently utilized with fewer trainedpersonnel.

SUMMARY OF INVENTION The object of the present invention is to providean accurate method for sampling mixtures of sulfur compounds andseparating, identifying and quantitatively monitoring each sulfurcompound. This invention is particularly applicable to concentrations ofsulfur compounds in the low parts per billion range.

Especially with respect to ambient air containing sulfur compounds, afurther object of this invention is to provide a flexible method wherebygas samples can be taken in the field and then analyzed at a differentlocation at some later time without any deterioration ofthe sample.

These objects can be obtained by impinging gaseous samples containingsulfur compounds into sulfur-free methanol. The methanol solution isthen inserted into a gas chromatograph column where the sulfur compoundsare separated. The sulfur compounds are then identified and measuredquantitatively by first passing the separated compounds through apyrolysis furnace where they are oxidized to sulfur dioxide, and then bypassing the sulfur dioxide products into a titration cell where they aretitrated coulometrically.

The use of methanol as the solvent for sulfur compounds obviates some ofthe problems of prior art methods. It has been found that sulfurcompounds are completely soluble in methanol and do not adhere to orreact with the sample container walls. Moreover, there is no reaction ofthe sulfur compounds with the methanol or with the other compounds insolution. Consequently, much flexibility in the sampling and analyzingof mixtures of sulfur compounds is obtained, as the samples can beaccurately analyzed many days, or even weeks, after they are taken.

To separate carbonyl sulfide, hydrogen sulfide and various organicsulfur compounds, the gas chromatograph column must be inert to both thesulfur compounds and the methanol. A column packed withoctylphenoxypolyethylcne oxyethanol on polytetrafluoroethylenesurprisingly fulfills this criteria. By absorbing the sulfur compoundsin methanol, the previous problem of retention of appreciable quantitiesof gaseous sulfur compounds in the column is obviated.

The use of this gas chromatograph column in conjunction with amicrocoulometer provides a means for quickly separating, identifying andquantitatively monitoring mixtures of sulfur compounds at low parts perbillionlevels in a matter of4 to 5 minutes.

This invention also provides a quick simple method for the analysisofthiophene and other heterocyclic compounds, even though thesecompounds are normally found as impurities in solid rather than gaseousmaterials.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE presents a simplified flowdiagram of the method ofthis invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The preferred embodiment of thisinvention consists of a method whereby low concentrations ofodor-causing sulfur compounds in ambient air can be accurately sampledand analyzed. Such a method will allow air pollution control agencies toscientifically characterize low levels of these sulfur compounds andthereby regulate the emission os odors resulting from such compounds.Moreover, this method will aid in the development of techniques to abatethe emission of odorcausing sulfur compounds.

The procedure in accordance with this invention consists of passing ameasured amount of a gaseous mixture containing sulfur compounds throughsubstantially sulfur-free methanol; passing the methanol solution inwhich the sulfur compounds have been absorbed through a gaschromatograph, essentially inert to methanol and sulfur compounds, toseparate the sulfur compounds; passing the sulfur compounds as they areemitted from the gas chromatograph column through a pyrolysis furnace tooxidize each compound to sulfur dioxide; and passing the oxidized sulfurcompounds as they are emitted from the furnace through a microcoulometerwhere they are titrated to determine the concentration of each sulfurcompound in the gaseous mixture. This procedure provides an accuratemethod for sampling, separating, identifying and quantitativelymonitoring sulfur compounds in the parts per billion range.

By using methanol as the solvent or scrubbing solution, the sulfurcompounds are prevented from reacting with or adhering to the walls ofthe sampling containers. No reaction between the sulfur compounds orbetween the sulfur compounds and the methanol has been observed.

To test the solvent capacity of methanol for sulfur compounds, gassamples containing sulfur compounds were impinged through two samplescrubbers in series. No sulfur compounds were detected in the methanolin the second scrubber, thus indicating that all of the sulfur compoundshad been absorbed by the methanol in the first scrubber.

Although heavier alcohols, such as ethanol, propanol or butanol, orethyl ether, can be used instead of methanol, they are not preferredsince methanol is the best solvent and has fewer carbon atoms which canbe oxidized to carbon dioxide in the pyrolysis furnace. The presence ofmore than small amounts of carbon dioxide interferes with the titrationin the microcoulometer.

The methanol used must be essentially sulfur free, as any sulfur presentin the methanol will indicate a higher than actual concentration. It hasbeen found that high purity, sulfurfree methanol can be more readilyobtained than other sulfurfree alcohols or others.

Gas samples may be obtained by using conventional impinger gas samplers,such as a Mine Safety Appliance midget impinger. The use of such animpinger allows the volume of gas sampled and passed through thesulfur-free methanol scrubbing solution to be measured.

The absorption of the sulfur compounds in methanol allows greaterflexibility in the sampling and analysis of gaseous sulfur compounds,especially in air pollution control work. For example, ambient aircontaining sulfur compounds can be sampled in the field and then takento a laboratory for analysis at a later time. Even over an extendedperiod of time, no deterioration of the sample occurs. In contrast, ithas been found that one part per million of hydrogen sulfide insertedinto a conventional three liter polyethylene gas sampling bag cannot bedetected on analysis. This results from the hydrogen sulfide reactingwith or adhering to the walls of the sampling bag. This does not occurwhen the gas sample is passed through methanol. Neither is there anyinteraction of the sulfur compounds. In fact, the stability of methanolsolutions containing sulfur compounds is such that the solutions can beused as reference samples for calibrating the analytical equipment.

With this flexibility, a substantial cost savings can be realized byreducing the number of analytical equipment units and the number oftrained operators of the equipment. For instance, if a sampledeteriorates over a short period of time either by reaction with oradherence to the walls of the container, analytical equipment would needto be placed into the field at the point of sampling in order tomaintain the accuracy required at parts per billion levels. On the basisof the number of samples taken and analyzed, such a use of theanalytical equipment would require more equipment and more trainedpersonnel as compared to having the samples taken in the field byrelatively untrained personnel and then analyzed at a centrallaboratory. Moreover, the analytical equipment cannot be as efficientlyutilized in the field as in a laboratory as much time is lost in movingthe equipment from sampling point to sampling point. This movement ofthe equipment of the analytical equipment would also necessitate morecalibration and maintenance of the equipment. Obviously, inaccuratemeasurements resulting from leakage of the surrounding atmosphere intothe equipment can be minimized by using the equipment in an essentiallysulfurfree laboratory atmosphere than in the atmosphere being sampled.

The analytical equipment used in accordance with the preferredembodiment of the present invention is shown diagrammatically in theFIGURE and consists of gas chromatograph column 1, pyrolysis furnace 2and microcoulometer 3. The sample methanol solution containing sulfurcompounds is inserted into chromatograph column 1 through line 4. Alsoadded to column 1 is the helium carrier gas. The sulfur compounds asseparated in column 1 then flow through line 5 into pyrolysis furnace 2,to which is also added oxygen through line 6. The separated sulfurcompounds as oxidized to sulfur dioxide in furnace 2 then pass throughline 7 into microcoulometer 3. The results of the analysis bymicrocoulometer 3 are usually visually recorded by a recording device,such as recorder 8, which is connected to the microcoulometer. Theformula for calculating the concentration of each sulfur compound in thesample will be described hereinafter.

Besides having the capability of separating sulfur compounds, the gaschromatograph column and its contents must he inert to methanol andsulfur compounds. Such a column is u lll foot stainless steelone-fourth-inch column packed with oc-tylphenoxypolyethylene oxyethanolon polyte'trnfluoroethylene. The introduction of the sulfur compoundsinto the column in in methanol solution instead of in a gaseous formprevents the compounds from reacting with or adhering to the packing orthe walls of the column. Helium is used as a carrier gas at flow ratesfrom about 90 to about 170 milliliters per minute. The temperature atwhich the column is maintained is not critical but it must be highenough to prevent adherence of the sulfur compounds to the column wallsor the packing but not so high as to cause the packing to break down.The gas chromatograph is typically operated at about 145C. However, asshown by Table 1 below, the relative retention times of sulfur compoundsin methanol are somewhat variable at different column temperatures.

TABLE I Retention Time in Seconds The compounds having approximately thesame retention times can be distinguished and identified by useofwell-known sample dilution and temperature programming techniques.

The sulfur compounds as they are emitted from the gas chromatographcolumn in the relation shown in Table 1 above are then passed into apyrolysis furnace where they are oxidized in oxygen at such atemperature as to form sulfur dioxide. The temperature must bemaintained low enough to avoid the formation of sulfur trioxide but highenough to avoid the formation of sulfides. Both sulfides and sulfurtrioxide have an adverse effect on the titration cell reactions. Thepreferred temperature range is from about 675C. to about 725C. Thefollowing reactions are typical of those occurring in the furnace:

The sulfur compounds, as separated and oxidized, are then passed into aconventional microcoulometer where the sulfur dioxide products aretitrated with either iodine or bromine ions. In the preferred iodinecell, the contents consist of sodium azide as the buffer solution,potassium iodide, acetic acid and iodine. As the separated, oxidizedsulfur compounds are drawn through the cell at a constant rate, thetriiodide ions in the electrolyte are consumed The resultant drop intriiodide ion concentration is sensed as a drop in cell voltage and thetriiode ion generating circuit is activated to restore the original cellvoltage. The additional current flow through the generating circuit isproportioned to the quantity of triiodide ion-titrable gases reacting inthe cell. The reaction at the reference sensor electrode is as follows:

S0 l] H O S0 3l' 2H At the generator anode, the reaction to replace thedepleted triiodide ions is as follows:

I, l =l- The titration cell contents must be replenished periodically tomaintain an approximate concentration of 0.07 percent acetic acid, 0.05percent potassium iodide and 0.07 percent sodium azide. Theconcentration of these three cell components is especially affected bythe presence of substantial amounts of amines and organic chlorides inthe samples. Upon combustion, the amines form nitrogen oxides and theorganic chlorides form acids, both of which react with the cellsolution.

A sample of a methanol solution containing sulfur compounds can becompletely analyzed by the described gas chromatograph, pyrolysisfurnace and microcoulometer arrangement in an average of4 to 5 minutes.The results of the analysis are visually recorded on a strip chart bymeans of a record ing instrument connected to the microcoulometer. Usingthe relative retention times of the sulfur compounds in the gaschromatograph column, the peaks on the recorder strip chart can beidentified as representing specific sulfur compounds. The concentrationof each sulfur compound is determined by the following formula:

Peak height in millimeters X factor (cpncemrdnon micrograms permicroliters of sample resistance microhter) in ohms (microcoulometer)The factor for each sulfur compound was determined by running samples ofknown concentrations. Factors have been obtained as set forth in Tablell:

TABLE ll Compound Factor Carbonyl sulfide 0.264 Hydrogen sulfide 102Sulfur dioxide 0.246 Ethyl mercaptan l L9 Dimethyl sulfide 0.057 Methylmercaptan [0.4 Diethyl disulfide 2.32 Diethyl sulfide 0.956 Dimethyldisulfide 0.228 Thiophene 0.651 2-bromothiophene 7.069 Z-nitrothiopheneL360 Z-acetylthiophene 3.552 2-thiophenecarboxaldehyde 5.575Z-thiophenecarboxylic acid 2.095

The accuracy of the method in accordance with this invention forsampling and analyzing sulfur compounds is shown by Table III. Knownamounts of sulfur compounds inserted into sulfur-free methanol wereanalyzed using the method previously described.

TABLE III Compound Micrograms taken Micrograms recovered Dimethylsulfide 0.085 0.085 Diethyl sulfide 0.043 0.044 Dimethyl disulfide 0.01I 0.012 Diethyl disulfidc 0.027 0.026 Ethyl mercaptan 0.092 0.09]

Hydrogen sulfide 0.095 0.096 Carbonyl sulfide 0.084 0.084 Methylmercaptan 0.084 0.084 Sulfur dioxide 0.108 0.106 Thiophene O. |9l 0.176

This invention can also be applied to the detection and analysis ofsulfur compound impurities in solid materials. The same procedure aspreviously described for gaseous mixtures is used in sampling andanalyzing the materials. Obviously, the material to be analyzed must beofa small enough particle size to insure that all the sulfur compoundsare completely dissolved in the methanol.

in the analysis of the solid materials, this invention has been found tobe particularly applicable to the sampling and analysis of lowconcentrations of thiophene and other heterocyclic sulfur compounds insynthetic rubber products. Previously, very sophisticated and expensiveequipment was required to separate, identify and quantitatively monitorthese compounds. However, the method according to this invention allowsthe analysis of these compounds to be effected very quickly withrelatively inexpensive equipment.

It would be obvious to persons skilled in the art that minor variationsin the procedures of this invention may be used to sample and analyzesulfur compounds in gaseous mixtures or solid materials in addition tothose specifically set forth and that changes and modifications of theinvention can be made. lnsofar as such variations and modificationsincorporate the true spirit of this invention, they are intended to beincluded within the scope of the appended claims.

lclaim:

l. The method of sampling a gaseous mixture containing lowconcentrations of sulfur compounds for the analysis of said sulfurcompounds comprising passing a measured amount of said gaseous mixturethrough substantially sulfur-free methanol to absorb essentially all thesaid sulfur compounds in the said methanol.

2. The method according to claim 1 wherein said gaseous mixture isambient air containing parts per billion concentrations of odor-causingsulfur compounds.

3. The method of sampling and analyzing a gaseous mixture containing lowconcentrations of sulfur compounds comprising the successive steps of:

a. passing a measured amount of said gaseous mixture throughsubstantially sulfur-free methanol to absorb essentially all the saidsulfur compounds in the methanol;

b. passing the methanol containing the absorbed sulfur compounds througha gas chromatograph column essentially inert to methanol and sulfurcompounds in methanol to separate the sulfur compounds;

0. oxidizing the sulfur compounds as separated to form sulfur dioxide;and

d. titrating the separated, oxidized sulfur compounds in the form ofsulfur dioxide in a microcoulometer to thereby determine theconcentration of each sulfur compound in the gaseous mixture.

4. The method according to claim 3 wherein the gaseous mixture isambient air containing parts per billion concentrations ofodor-causingsulfur compounds.

5. The method according to claim 3 wherein the separated, oxidizedsulfur compounds in the form of sulfur dioxide are titrated with iodideions in a microcoulometer.

6. The method according to claim 5 wherein the sulfur compounds asseparated are oxidized at a temperature in the range from about 675C. toabout 725C. to form sulfur dioxide.

7. The method of sampling, separating and quantitatively measuring lowconcentrations of sulfur compounds in a gaseous mixture comprising thesuccessive steps of:

a. passing a measured amount of said gaseous mixture throughsubstantially sulfur-free methanol to absorb essentially all the saidsulfur compounds in the methanol;

b. passing the methanol containing the absorbed sulfur compounds througha gas chromatograph column packed with octylphenoxypolyethyleneoxyethanol on polytetrafluoroethylene to separate the sulfur compounds;

c. oxidizing the sulfur compounds as separated to form sulfur dioxide;and

d. titrating the separated, oxidized sulfur compounds in the form ofsulfur dioxide with iodide ions in a microcoulometer to therebydetermine the concentration of each sulfur compound in the gaseousmixture.

8. The method according to claim 7 wherein the gaseous mixture isambient air containing parts per billion concentrations of odor-causingsulfur compounds, and the sulfur compounds as separated are oxidized ata temperature in the range from about 675C. to about 725C. to formsulfur dioxide.

9. The method according to claim 8 wherein the sulfur compounds areheterocyclic sulfur compounds; the heterocyclic sulfur compounds asseparated are oxidized at a temperature in the range from about 675C. toabout 725C. to form sulfur dioxide; and the separated, oxidizedheterocyclic sulfur compounds in the form of sulfur dioxide are titratedwith iodide ions in a microcoulometer.

10. The method of sampling and analyzing a solid material containing lowconcentrations of sulfur compounds comprising the successive steps of:

a. dissolving a measured amount of said solid material in substantiallysulfur-free methanol to absorb essentially all the said sulfur compoundsin the methanol;

b. passing the methanol containing the absorbed sulfur compounds througha gas chromatograph column essentially inert to methanol and sulfurcompounds in methanol to separate the sulfur compounds;

0. oxidizing said sulfur compounds as separated to form sulfur dioxide;and

d. titrating the separated, oxidized sulfur compounds in the form ofsulfur dioxide in a microcoulometer to thereby determine theconcentration of each sulfur compound in said solid material.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORREQTION Patent NO. 3,Dated I Inventor(s) Ewin A. Eads It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

In the Abstract, line 7, the word "on" should come after oxyethanol Inthe Abstract, lines 7 and 8, "polytetrafluoroehtylene" should bepolytetrafluoroethylene Col. 2, line 19, "therefor" should be thereforeCol. 2, line 30, "X-30 S" should be X-305 Col 2, line 30, "or" should beon Col. 2 line 31, "(polytetraflouroethylene)" should be(polytetrafluoroethylene) Col. 3, line 57, "as should be of Col. 6, line6, "2H should be 2H Col. 6, line 31, (concentration micrograms permicroliter) should be concentration (micrograms per microliter) Signedand sealed this 18th day or July 1972.

(SEAL) Attest:

EDWARD MFLETCHER,JR. RCBERT GOTTSCHALK Attesting OfYioer Commissioner ofPatents FORM P0405) (10459) USCOMM-DC some-ps9 ".5. GOViRNMENT PRYN'HNGOFF'CEZ I959 0-366-335

2. The method according to claim 1 wherein said gaseous mixture isambient air containing parts per billion concentrations of odor-causingsulfur compounds.
 3. The method of sampling and analyzing a gaseousmixture containing low concentrations of sulfur compounds comprising thesuccessive steps of: a. passing a measured amount of said gaseousmixture through substantially sulfur-free methanol to absorb essentiallyall the said sulfur compounds in the methanol; b. passing the methanolcontaining the absorbed sulfur compounds through a gas chromatographcolumn essentially inert to methanol and sulfur compounds in methanol toseparate the sulfur compounds; c. oxidizing the sulfur compounds asseparated to form sulfur dioxide; and d. titrating the separated,oxidized sulfur compounds in the form of sulfur dioxide in amicrocoulometer to thereby determine the concentration of each sulfurcompound in the gaseous mixture.
 4. The method according to claim 3wherein the gaseous mixture is ambient air containing parts per billionconcentrations of odor-causing sulfur compounds.
 5. The method accordingto claim 3 wherein the separated, oxidized sulfur compounds in the formof sulfur dioxide are titrated with iodide ions in a microcoulometer. 6.The method according to claim 5 wherein the sulfur compounds asseparated are oxidized at a temperature in the range from about 675*C.to about 725*C. to form sulfur dioxide.
 7. The method of sampling,separating and quantitatively measuring low concentrations of sulfurcompounds in a gaseous mixture comprising the successive steps of: a.passing a measured amount of said gaseous mixture through substantiallysulfur-free methanol to absorb essentially all the said sulfur compoundsin the methanol; b. passing the methanol containing the absorbed sulfurcompounds through a gas chromatograph column packed withoctylphenoxypolyethylene oxyethanol on polytetrafluoroethylene toseparate the sulfur compounds; c. oxidizing the sulfur compounds asseparated to form sulfur dioxide; and d. titrating the separated,oxidized sulfur compounds in the form of sulfur dioxide with iodide ionsin a microcoulometer to thereby determine the concentration of eachsulfur compound in the gaseous mixture.
 8. The method according to claim7 wherein the gaseous mixture is ambient air containing parts perbillion concentrations of odor-causing sulfur compounds, and the sulfurcompounds as separated are oxidized at a temperature in the range fromabout 675*C. to about 725*C. to form sulfur dioxide.
 9. The methodaccording to claim 8 wherein the sulfur compounds are heterocyclicsulfur compounds; the heterocyclic sulfur compounds as separated areoxidized at a temperature in the range from about 675*C. to about 725*C.to form sulfur dioxide; and the separated, oxidized heterocyclic sulfurcompounds in the form of sulfur dioxide are titrated with iodide ions ina microcoulometer.
 10. The method of sampling and analyzing a solidmaterial containing low concentrations of sulfur compounds comprisingthe successive steps of: a. dissolving a measured amount of said solidmaterial in substantially sulfur-free methanol to absorb essentially allthe said sulfur compounds in the methanol; b. passing the methanolcontaining the absorbed sulfur compounds through a gas chromatographcolumn essentially inert to methanol and sulfur compounds in methanol toseparate the sulfur compounds; c. oxidizing said sulfur compounds asseparated to form sulfur dioxide; and d. titrating the separated,oxidized sulfur compounds in the form of sulfur dioxide in amicrocoulometer to thereby determine the concentration of each sulfurcompound in said solid material.